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Category:   OS (Microsoft)  >   Windows NTFS Vendors:   Microsoft
(Microsoft Issues Fix Instructions) Windows 2000 Operating System Default Permissions for the System Partition Lets Local Users Bypass Individual File Permissions and Replace Key System Files
SecurityTracker Alert ID:  1005500
SecurityTracker URL:  http://securitytracker.com/id/1005500
CVE Reference:   CVE-2002-1184   (Links to External Site)
Date:  Oct 31 2002
Impact:   Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A default configuration vulnerability was reported in Windows 2000. A local user in the 'Everyone' group can replace files in the system partition.

SECURITY.NNOV reported that the Windows 2000 system partition uses weak default permissions. According to the report, the system partition itself has 'Everyone/Full Control' access permissions by default. Users with Full Control NTFS permissions for a folder can reportedly delete any file from the folder regardless of the individual file permissions (this is reportedly for POSIX compliance).

A local user can gain ownership rights and get full control over any system file located in root of system partition. A demonstration exploit transcript is provided:

1. Delete the target file (delete the file rather than placing it in the recycle bin, because additional permissions are required to place files in the recycle bin requires read permission).

2. Create a new file with the same name as the previously deleted file. The local user is now the owner of this newly created file and has Full Control permission for this file inherited from root folder.

A local user can replace critical system files with trojan files.

Another user has separately reported that this behavior may occur if the Windows installation is upgraded from a previous operating system (e.g., NT). However, if the system disks on Windows systems are re-formatted during Windows 2000 setup (i.e., clean-installed workstations and servers) the user reports that NTFS permissions will be hardened for the system partition.

Impact:   A local user in the 'Everyone' group can replace files in the system partition.
Solution:   Microsoft recommends that administrators consider changing access permissions on the Windows 2000 system root directory. There is no patch for this. Instead, an administrative procedure is required to correct the issue.

The required changes are discussed in the "Frequently Asked Questions" section of the Microsoft security bulletin MS02-064, available at:

http://www.microsoft.com/technet/security/bulletin/MS02-064.asp

Microsoft suggests that the default permissions for Windows XP may be a good guide for setting permissions (however, Microsoft notes that the appropriate settings will depend on customer-specific requirements). The default permissions for the root directory on the system drive for Windows XP are reported to be:

- Administrators: Full (This Folder, Subfolder and Files)
- Creators Owners: Full (Subfolders and Files)
- System: Full (This Folder, Subfolder and Files)
- Everyone: Read and Execute (This Folder Only)

Microsoft plans to issue Knowledge Base article Q327522 regarding this issue, to be available shortly on the Microsoft Online Support web site at:

http://support.microsoft.com/?scid=fh;en-us;kbhowto

Vendor URL:  www.microsoft.com/technet/security/bulletin/MS02-064.asp (Links to External Site)
Cause:   Access control error
Underlying OS:  Windows (2000)

Message History:   This archive entry is a follow-up to the message listed below.
Aug 4 2002 Windows 2000 Operating System Default Permissions for the System Partition Lets Local Users Bypass Individual File Permissions and Replace Key System Files



 Source Message Contents

Subject:  Microsoft Security Bulletin MS02-064: Windows 2000 Default Permissions Could Allow Trojan Horse Program (Q327522)


-----BEGIN PGP SIGNED MESSAGE-----

- ----------------------------------------------------------------------
Title:      Windows 2000 Default Permissions Could Allow Trojan Horse
            Program (Q327522)
Date:       30 October 2002
Software:   Windows 2000
Impact:     Trojan Horse program execution 
Max Risk:   Moderate
Bulletin:   MS02-064

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS02-064.asp.
- ----------------------------------------------------------------------

Issue:
======
On Windows 2000, the default permissions provide the Everyone group
with Full access (Everyone:F) on the system root folder
(typically, C:\). In most cases, the system root is not in the search
path. However, under certain conditions - for instance, during logon
or when applications are invoked directly from the Windows desktop
via Start | Run - it can be. 

This situation gives rise to a scenario that could enable an attacker
to mount a Trojan horse attack against other users of the same
system, by creating a program in the system root with the same name
as some commonly used program, then waiting for another user to
subsequently log onto the system and invoke the program. The Trojan
horse program would execute with the user's own privileges, thereby
enabling it to take any action that the user could take. 

The simplest attack scenario would be one in which the attacker knew
that a particular system program was invoked by a logon script. In
that case, the attacker could create a Trojan horse with the same
name as the system program, which would then be executed by the
logon script the next time someone logged onto the system. Other
scenarios almost certainly would require significantly greater user
interaction - for instance, convincing a user to start a particular
program via Start | Run - and would necessitate the use of social
engineering. 

The systems primarily at risk from this vulnerability would be
workstations that are shared between multiple users, and local
terminal server sessions. Other systems would be at significantly
less risk: 

 - Workstations that are not shared between users would be at no
   risk, because the attacker would require the ability to log onto
   the system in order to place the Trojan horse. 

 - Servers would be at no risk, if standard best practices have
   been followed that advocate only allowing trusted users to log
   onto them. 

 - Remote Terminal server sessions would be at little risk,
   because each user's environment is isolated. That is, the system
   root is never the current folder - instead, the user's Documents
   and Settings folder is, but the permissions on this folder would
   not enable an attacker to place a Trojan horse there. 

Mitigating Factors:
====================
 - An attacker would require the ability to log onto the system
   interactively in order to place the Trojan horse program. It
   could not be placed remotely 

 - As discussed above, dedicated workstations, servers and remote
   terminal server sessions would be at less risk (or, in some cases,
   none at all) from the vulnerability. 

Risk Rating:
============
 - Internet systems: Low
 - Intranet systems: Low
 - Client systems: Moderate

Patch Availability:
===================
 - This vulnerability requires an administrative procedure rather
   than a patch. The needed changes are discussed in the FAQ.  
   Please read the Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-064.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Jason Miller of Security Focus (http://www.securityfocus.com)

- ---------------------------------------------------------------------

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT 
SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY
DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

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